/**
 * Behaves the same as setInterval except uses requestAnimationFrame() where possible for better performance
 * @param {function} fn The callback function
 * @param {int} delay The delay in milliseconds
 */
window.requestInterval = function(fn, delay) {
	if( !window.requestAnimationFrame     && 
		!window.webkitRequestAnimationFrame && 
		!window.mozRequestAnimationFrame    && 
		!window.oRequestAnimationFrame      && 
		!window.msRequestAnimationFrame)
			return window.setInterval(fn, delay);
	var start = new Date().getTime(),
		handle = new Object();
	function loop() {
		var current = new Date().getTime(),
			delta = current - start;
		if(delta >= delay) {
			fn.call();
			start = new Date().getTime();
		}
		handle.value = requestAnimFrame(loop);
	};
	handle.value = requestAnimFrame(loop);
	return handle;
}

/**
 * Behaves the same as clearInterval except uses cancelRequestAnimationFrame() where possible for better performance
 * @param {int|object} fn The callback function
 */
window.clearRequestInterval = function(handle) {
    window.cancelAnimationFrame ? window.cancelAnimationFrame(handle.value) :
    window.webkitCancelRequestAnimationFrame ? window.webkitCancelRequestAnimationFrame(handle.value)	:
    window.mozCancelRequestAnimationFrame ? window.mozCancelRequestAnimationFrame(handle.value) :
    window.oCancelRequestAnimationFrame	? window.oCancelRequestAnimationFrame(handle.value) :
    window.msCancelRequestAnimationFrame ? msCancelRequestAnimationFrame(handle.value) :
    clearInterval(handle);
};